Timing of intrapartum ampicillin and prevention of vertical transmission of group B streptococcus.
OBJECTIVE
To evaluate the relationship between the time elapsed from the administration of ampicillin prophylaxis to delivery and its efficacy in interrupting intrapartum transmission of group B streptococcus.


METHODS
During the 12-month study period, all women who came to the Virgen de las Nieves Hospital (Granada, Spain) for delivery were screened for group B streptococcus vaginal carriage by a pigment-detection culture-based procedure. Colonized women were treated with ampicillin (2 g intravenously), and the interval between ampicillin administration and delivery was recorded. Newborns from colonized mothers also were screened to detect group B streptococcus colonization.


RESULTS
During the study period, 4525 women were admitted to the hospital for delivery and screened for group B streptococcus vaginal colonization. Group B streptococcus was detected in 543 women (12%), of whom 454 gave birth vaginally to 454 liveborn infants. Intrapartum ampicillin was given to 201 of these 454 women (44%), and 10% of the newborns from mothers who received intrapartum ampicillin prophylaxis were colonized by group B streptococcus. The relationship between timing of ampicillin administration and rate of neonatal group B streptococcal transmission was as follows: less than 1 hour before delivery, 46%; 1-2 hours, 29%; 2-4 hours, 2.9%; and more than 4 hours, 1.2%. Among the 253 mothers who received no intrapartum prophylaxis, colonization was found in 120 of their newborns (47%).


CONCLUSIONS
When the time between the start of ampicillin prophylaxis and delivery is at least 2 hours, vertical transmission of group B streptococcus is minimized.
de Cueto
M
M
Department of Obstetrics and Gynaecology, Virgen de las Nieves Hospital, Granada, Spain.
Sanchez
M J
MJ
Sampedro
A
A
Miranda
J A
JA
Herruzo
A J
AJ
Rosa-Fraile
M
M
D000667:Ampicillin / Q000008:administration & dosage* / Q000627:therapeutic use; D002353:Carrier State / Q000188:drug therapy*; D005260:Female; D006801:Humans; D007231:Infant, Newborn; D018445:Infectious Disease Transmission, Vertical / Q000517:prevention & control* / Q000706:statistics & numerical data; D007275:Injections, Intravenous; D007745:Labor Onset; D010406:Penicillins / Q000008:administration & dosage* / Q000627:therapeutic use; D011247:Pregnancy; D011251:Pregnancy Complications, Infectious / Q000188:drug therapy*; D011446:Prospective Studies; D013290:Streptococcal Infections / Q000188:drug therapy / Q000517:prevention & control*; D013292:Streptococcus agalactiae / Q000302:isolation & purification / Q000472:pathogenicity*; D013997:Time Factors; D014621:Vagina / Q000382:microbiology
D010406:Penicillins; D000667:Ampicillin